Using QUnit 2.x assert.async() to test ajax calls

Question

I'm using QUnit 2.0.1 to unit test an existing code base. I've got a function that makes an ajax call and then enables a button and sets a boolean. I'm trying to write a QUnit test to assert that the button is enabled and the boolean is false after calling the function.

My function with the ajax call:

self.saveComment = function() {     
    if(self.isEditing())
    {   
        $('#saveCommentButton').attr('disabled', 'disabled');

        var comment = self.newComment();            
        var data = {
                newCommentText : comment,
                objectId: objectId,
                objectType : objectTypeId
        };

        $.ajax({
            type: "POST",
            url: "addBOComment.action",
            data: data,
            success: function(comments){
                self.comments(comments);                    
                $('#saveCommentButton').attr('enabled', 'enabled');
                self.isEditing(false);                  
            }
        });         
    }
};

My QUnit test:

QUnit.test("test saveComment() - async", function(assert){      
    $('#qunit-fixture').append('<input type="button" id="saveCommentButton" disabled="disabled"/>')

    model.isEditing(true);
    model.newComment("qunit test for comments");

    var done = assert.async();

    window.setTimeout(function() {
     model.saveComment(); //function with ajax call
     assert.equal(model.isEditing(), false, 'success');
     assert.equal($('#saveCommentButton').attr("enabled"), "endabled", 'success');  
     done();

   }, 150);

});

The test runs, but success is never called so my button is disabled and my boolean is still true. What am I doing wrong?